In recent years, with the spread of radio terminals such as smartphones capable of executing a lot of applications, the frequency at which a radio terminal connects to a network and the frequency at which a network performs paging of a radio terminal are increasing.
Therefore, in a mobile communication system, network load accompanying signaling is increasing. In view of such a situation, techniques for reducing signaling are being studied in the 3rd Generation Partnership Project (3GPP), which is the standardization project for mobile communication systems.